It appears there's also a season, or two, rather - Fall (Sep-Nov) and Spring (Feb-Apr) - for the full transit on the mainstream lines, compared with higher frequencies, probably year round, for the roundtrip Ft Lauderdale (partial transit).

Any recommendations on which season is better? Whether it's weather (pardon the pun), or whatever?

I'm concerned about the hurricane season.

There's a slew of full transits in September and April when ships reposition between Alaska and the Caribbean. Nonetheless, many of the lines also have a ship doing full transits all winter, though sometimes interspersed with other itineraries such as Hawai'i round trip from the Left Coast (also a great cruise, BTW).

The season really does not matter all that much. Hurricanes could disrupt a port of call in the fall, but they are less of a factor than on Caribbean itineraries because the ships on Panama Canal transits spend less time in the Caribbean.